1. Field of the Invention
The present invention relates to a circuit device and more particularly relates to a circuit device including a hybrid integrated circuit consisting of a large number of circuit elements such as a semiconductor element.
2. Description of the Related Art
With reference to FIG. 7, a configuration of a conventional hybrid integrated circuit device 100 will be described. This technology is described for instance in Japanese Patent Application Publication No. Hei 5 (1993)-102645. Conductive patterns 103 are formed on a surface of a rectangular board 101 with an insulating layer 102 interposed therebetween. Circuit elements are fixed to desired spots of the conductive patterns 103 to form a predetermined electric circuit. Here, as the circuit elements, a semiconductor element 105A and a chip element 105B are connected to the conductive patterns 103. Leads 104 are connected to pads 109, and function as external terminals. The pads 109 are made of the conductive patterns 103 formed in a peripheral portion of the board 101. A sealing resin 108 has a function to seal the electric circuit formed on the surface of the board 101.
The semiconductor element 105A is, for example, a power element through which a large current of 1 ampere or more passes and has a very large heat value. Thus, the semiconductor element 105A is placed above a heat sink 110 mounted on the conductive pattern 103. The heat sink 110 is formed of a metal piece such as copper having a size of the order of length×width×thickness=10 mm×10 mm×1 mm, for example. By adopting the heat sink 110, heat generated from the semiconductor element 105A can be actively released to the outside. Furthermore, although not shown in FIG. 7, an LSI having a large number of electrodes provided on its surface is provided as a circuit element on an upper surface of the board 101.
In the hybrid integrated circuit device 100 having the above configuration, all the elements constituting a hybrid integrated circuit are disposed on the upper surface of the board 101. Since the board 101 is made of metal having excellent heat release properties, heat generated from the circuit elements such as the semiconductor element 105A is favorably released to the outside through the board 101.
However, the circuit elements mounted on the board 101 also include those having a very small heat value, such as a small signal semiconductor element. Such a circuit element having a small heat value is not required to be mounted on the board 101 made of metal having excellent heat release properties. The mounting of the circuit element, for which heat release is not required, on the upper surface of the circuit board 101 as described above leads to a problem that substantial packaging density on the upper surface of the board 101 is reduced.
Furthermore, when the LSI or the like is disposed near the semiconductor element 105A having a very large heat value, heat generated from the semiconductor element 105A is conducted through the board 101 having excellent thermal conductivity. Thus, there is also a risk that the LSI is heated by the heat, so that characteristics thereof are deteriorated.